The characters of “A Certain Scientific Railgun” wield amazing esper powers, but few are more impressive than our protagonist, Mikoto Misaka, nicknamed “the Railgun.” Her electricity powers, based on the electromagnetic projective launcher of the same name, allow her to shoot small arcade coins at high speeds for maximum damage. In other words, she’s kind of a badass.

But what exactly is a railgun? In celebration of the release of A Certain Scientific Railgun on DVD tomorrow, we’ve asked Justin Lan, a mechanical engineer from MIT, to explain the concept—-and how it relates to the show.

Warning: Those of you with an aversion to science and/or math may wish to turn back now, but if you stick around you might just learn something.

The main character, Mikoto Misaka, has electromagnetic manipulation as a superpower. Her “signature” move is to take a coin, and to flick it forward while using her powers to accelerate it towards the target; as a result, she has earned the nickname “The Railgun”. Or, bug zapper, as Toma so affectionately calls her.

To the right you will see what an actual railgun looks like (source Wikipedia)

So, now let’s find out how one works! Essentially, when you run a current through a loop of wire, it produces a magnetic field ( B ) in the loop. This field interacts with the current going through the loop to produce a force that pushes outwards on the loop (relative to the center of the loop). It doesn’t matter which way the current is going.

If you run a lot of current through the loop, the loop rips apart due to the forces! Well, it would, except usually what happens is that all the current going through the wires instead causes the loop to catch fire and/or explode. Which isn’t good for anybody.

Let’s replace the loop with two long “rails” of metal parallel to each other bolted firmly to the ground, with a thing that can slide down the rails connecting them. When we turn the current on, each section of the loop tries to go outwards; the rails are bolted down, but the sliding object travels down the rails just fine due to the forces. Now, if you make the rails really long, you can use this system to go places, but it’ll require a lot of power.

If you make the rails a bit too short, the sliding object goes flying off the end. This is a railgun.

So how does this relate to Misaka’s powers?

The first thing, of course, is that Misaka’s ability doesn’t look anything like a railgun. Did you see any rails? I didn’t think so.

There are other ways of shooting projectiles using electricity, of course. Moving electric charges (currents) produce magnetic fields, so producing magnetic fields should be child’s play for Misaka. If she makes a giant magnetic field in the air, and makes a smaller magnetic field in the coin, the coin will go zipping through the air … along with every other magnetic object in the area.

Another possibility is that Misaka is effectively creating rails out of thin air by making the air conduct electricity and thus serving as rails. Normally, air doesn’t conduct electricity, which is why you don’t get zapped until you stick your finger in the electrical socket. However, at high enough voltages, the air becomes conductive, and electricity can arc through the air. This is why, even though current is what’s actually deadly, all of the warning signs near power stations read “DANGER: HIGH VOLTAGE”.

Arcs of electricity (like lightning bolts) are crooked, so this approach probably wouldn’t create very good rails. Most likely, Misaka uses the “make a magnetic field in the air” approach. If the magnetic field were sufficiently focused, she could accelerate only the coin and possibly a few nearby objects.

So now we have a solid idea of what a railgun is and, in theory, how Misaka uses it. We can also look at how much voltage she’s producing and the initial velocity of her shots. If you’re a little more scientifically-inclined, click this link for a PDF discussing more of these aspects.